Laminate system, a process for the production thereof and use thereof

ABSTRACT

In a system based on aluminum, zirconium and nitrogen at least one layer has covalent bonds of aluminum nitride or at least one layer has bonds of the aluminum nitride and zirconium nitride type. In a process for producing such a system an electrical gas discharge is fired in a vacuum chamber such as essentially to form a noble gas-enriched plasma resulting in ionization of the metal elements. To form the nitridic layer nitrogen is continuously fed as a reactive gas into the vacuum chamber and pumped away so as to set a reactive gas partial pressure which is used for process control purposes. The use of such a system for producing a coating on a surface is also described.

FIELD OF THE INVENTION

The invention relates to a laminate system based on aluminum, zirconiumand nitrogen, a process for the production of that laminate system by adeposit procedure, and the use of the laminate system.

BACKGROUND OF THE INVENTION

It is known for titanium nitride coatings to be applied to injectionmolding tools for the injection molding of plastic materials, in orderto reduce the level of coating deposit thereon, to improve the ease withwhich moldings can be removed from the molding tools, and to reduce theamount of tool wear. It has been found however that those titaniumnitride coatings are often not satisfactory in regard to theirproperties.

Coatings which are found to be an improvement in comparison with suchtitanium nitride coatings, in terms of the surface properties thereof,are those which contain chromium nitride as an essential constituentthereof. Chromium nitride-bearing coatings however suffer from thedisadvantage that the most important properties thereof tend topartially vary during the service life of the molding tools, for examplewhen assembling or vulcanizing rubber parts in which the chromiumnitride coatings lose their adhesion-inhibiting effect after a shortperiod of operation.

It is also known that zirconium nitride coatings can be applied toarticles in some cases as decorative coatings, by virtue of their brasscolorations. Those coatings admittedly in themselves form a hard surfaceand are chemically resistant to lyes, but they have in particular metalbonds.

Reference may be made to EP-A-0 603 486 describing a multi-stage processfor coating cutting and shaping tools with ternary hard-material layerassemblies or laminate structures such as titanium aluminum nitride,zirconium aluminum nitride or chromium aluminum nitride. Although thoselayer materials are admittedly suitable for tools for metal machining,they cannot however be used to real effect for reducing contact adhesionand for enhancing the chemical resistance of sensitive surfaces such asfor example plastic material extrusion tools which are polished to ahigh state of shine.

With those materials the solid laminate components involve predominantlymetal bonds, in which respect thorough and extensive scientific testshave demonstrated that all materials involving a predominantly metalbonding effect have a tendency to suffer from contact adhesion to agreater or lesser degree.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a laminate system whichcan at least markedly reduce the tendency to adhesion thereof and thedegree of deposit coating formation.

Another object of the present invention is to provide a layer orlaminate system which can afford a high level of corrosion resistanceand an enhanced degree of resistance to abrasion wear.

A further object of the present invention is to provide a laminatesystem which enjoys an enhanced surface quality in terms of reliabilityof manufacture, productivity and use-friendliness.

Yet another object of the present invention is to provide a laminatesystem which enjoys a low level of surface friction and an improvedrelease effect for example for the release of a molding from the surfacethereof.

Still a further object of the present invention is a process for theproduction of a laminate system which is simple to implement andreliable in terms of the production results.

Still another object of the present invention is to provide for the useof a laminate system on a workpiece such as to impart improved qualitiesand properties thereto.

In accordance with the principles of the present invention, in a firstaspect, the foregoing and other objects are attained by a layer orlaminate system based on aluminum, zirconium and nitrogen, wherein atleast one layer of the system has covalent bonds of aluminum nitride oraluminum nitride and zirconium nitride.

It has been found in that respect that in accordance with the inventionthe addition of zirconium nitride affords stabilization in respect ofthe covalent aluminum nitride bond, whereby it is possible to achieve ahigh level of chemical resistance. The choice of the chemicalcomposition adopted and the further alloying elements is effecteddepending on the respective properties required, in particular forexample in terms of minimizing adhesive forces upon coming into contactwith materials which have a tendency to adhere, more especially plasticmaterials such as thermosetting materials, thermoplastic materials,elastomers, resins, adhesives, rubber, caoutchouc, glass or aluminum.

The improved properties of a minimal tendency to adhesion, chemicalresistance in relation to lyes, the low coefficient of friction and thehigh level of resistance to wear afford components and members such asmolds which are provided with such coatings or laminate systemssignificantly higher levels of surface quality in regard tomanufacturing reliability, productivity and user-friendliness.

A preferred feature in accordance with the invention is for the atomicratio between aluminum and zirconium to be set at 1 or smaller, as thatcan greatly enhance the adhesive qualities of the coating according tothe invention.

In a preferred aspect of that feature the ratio between aluminum andzirconium is between 0.5 and 0.7, whereby the adhesion-inhibitingproperties of the system according to the invention, in relation tocoating deposits thereon, can be greatly enhanced.

An advantage of the laminate coating system according to the inventionin that respect is that it is optically transparent or at leastpartially translucent and/or electrically non-conductive or at least hasa high specific electrical resistance.

In accordance with a further embodiment the layer includes bonds of thealuminum nitride and zirconium nitride type, wherein desirably theatomic ratio between aluminum and zirconium is 1 or less. Preferably theatomic ratio between aluminum and zirconium is 0.5 or less, inparticular between 0.25 and 0.45, whereby the level of wear resistancecan be substantially enhanced and in particular it is possible to afforda high level of chemical resistance on the part of a coating produced inthat way.

In accordance with a preferred feature the coatings afforded by thelaminate system according to the invention are of a thickness of atleast 50 nm. In accordance with a preferred embodiment the coating is atleast between 200 nm and 2 μm thick for for example optical uses and tosatisfy the high demands in terms of surface quality or between 2 μm and6 μm for example for uses in plastic material processing, to avoidunwanted adhesion and coating deposit formation. Even a thickness ofover 6 μm with an additional abrasive loading on the coated surface ispossible.

In accordance with the invention it is possible to adjust the ohmicresistance of the coating according to the invention by suitableselection of the nitrogen component. Layers with a high proportion ofnitrogen have a high level of such resistance and thus a low level ofconductivity, whereas layers with a lower level of resistance have anitrogen content which is lower than the proportion of aluminum. In apreferred embodiment with a very low level of ohmic resistance the layeror layers essentially comprise or comprises pure aluminum or contains orcontain at least practically no nitrogen. Conversely, in the case ofcoatings with a high level of ohmic resistance, the layer or layers atleast predominantly comprises or comprise covalent bonds of aluminumnitride and zirconium nitride.

In accordance with the invention, for the purposes of increasingresistance to wear or chemical resistance, it can be provided that atleast two coatings are respectively arranged alternately, with layerswith a high proportion of nitrogen and layers with a low proportion ofnitrogen being deposited one upon the other. An advantage of such aconfiguration is the combination of different ones of theabove-mentioned properties in a laminate or layer system.

In that respect, the layer with a low level of ohmic resistance cancomprise a material which is a very good electrical conductor, inparticular gold, copper or pure aluminum. Conversely the layer with ahigh level of ohmic resistance can predominantly comprise an alloy basedon aluminum or plastic material or silicon or oxygen.

It will be appreciated that it is provided in accordance with theinvention that the coatings are arranged not alternately but in a randomsequence in dependence on the aims envisaged. Thus, one or more layerswith a high level of ohmic resistance can be followed by one or morelayers with a low level of ohmic resistance. An advantage of such aconfiguration is for example the possibility of producing sensor-actionsurfaces which for example with progressively increasing wear gain inelectrical conductivity or ohmic resistance. A further advantage in thisrespect is the possibility of selective or partial deposition of thecoatings according to the invention for example on semiconductors forthe production of conductor tracks and on ceramic or metal bodies assensor heads.

Depending on the desired purpose the invention further provides that thethicknesses of the individual layers of the structure relative to eachother may be varied.

In accordance with the principles of the present invention in a furtheraspect the foregoing and other objects are attained by a process for theproduction of a laminate system by deposit thereof, wherein anelectrical gas discharge is fired to form a plasma enriched with noblegas, for ionization of the aluminum and/or zirconium of the laminatesystem, in a vacuum chamber. To form the nitrides of the aluminum and/orzirconium nitrogen is continuously supplied and removed to adjust thereactive gas partial pressure as a regulatable parameter for processcontrol.

The nitrogen gas can be continuously supplied and removed by means of avacuum pump.

Reactive gases which can be used in accordance with the inventioninclude gases containing boron, silicon, carbon, oxygen and nitrogen andmixtures thereof and mixtures with further gases such as for examplenitrogen with ethane and/or silane and/or diborane and/or acetylene, ornitrogen with carbon dioxide. Preferably the gases, reactive and noblegas, are already in the ionized condition upon being introduced into thevacuum chamber. The at least one further reactive gas which can beintroduced into the vacuum chamber during the procedure for deposit ofthe coating system according to the invention can advantageously alsoalready be in an ionized condition upon being introduced into the vacuumchamber.

For the purposes of depositing the coatings according to the inventionit is provided that at least one respective target of aluminum and/or atarget of zirconium is arranged in the vacuum chamber. Alternatively itis possible, in place of a target of aluminum and a target of zirconium,to use an alloy consisting of aluminum and zirconium as the target. Theadvantage of that use of the targets in alloy form is the use of a solidalloy composition for the metal components and the greater ease ofcontrolling the manufacturing procedure.

In addition, in accordance with the invention, an additional targetcomprising at least one further material, preferably an element fromGroups IVa-VIa, Ib-IVb of the periodic system, can be arranged in thevacuum chamber. The invention also envisages the use of an alloycomprising at least two of those elements.

Zirconium-silicon or zirconium-boron or alloys comprising molybdenumand/or tungsten are referred to here by way of example.

Deposit of the coating is usually effected by way of magneticfield-assisted cathodic sputtering, with at least one sputtering cathodebeing regulated in a dc mode, a pulsed dc mode or in a HF or RF mode.When using electrically conductive materials or alloys the targetcathodes are preferably operated in the dc mode, while other alloys areoperated in the pulsed dc mode. Non-conducting targets are regulated inthe HF or RF mode. The procedure for deposit of the coating according tothe invention can also be implemented by means of an arc, light arc, ionbeam or electron beam vaporization method.

The layers according to the invention which are produced by the processaccording to the invention can be used for at least partial surfacecoating of materials. The materials that can be used in this respectinclude steel, aluminum, magnesium or copper alloys, silicon orsilicon-bearing materials, glass, ceramic, plastic material or sinteredhard substances, preferably carbide or cermet or fiber-reinforced glass.In particular such articles involve mold tools for processing plasticmaterial, rubber, caoutchouc or glass, tools for wood or aluminumworking, medical or surgical instruments, components for machines,engines, motors or automobiles, electrical or electronic components,ornaments such as jewelry or utility articles such as utensils and likecommodities. In that respect, it is immaterial whether the parts to beso coated are individual parts, composite parts or the entire parts ofthe above-indicated products.

The laminate system according to the invention comprising the at leastone coating can also advantageously be deposited on a component ormember which is already coated with any suitable layer, so that,depending on the atomic ratio of aluminum to zirconium the properties ofa high level of chemical resistance and/or a low level of tendency toadhesion can be applied to any desired workpiece.

EXAMPLE

A layer or laminate system based on aluminum, zirconium and nitrogen,which can be put to use for at least partial surface coating on amaterial, workpiece or like item. can be produced by a deposit processwherein an electrical gas discharge is fired to form a plasma enrichedwith noble gas, for ionization of aluminum and/or zirconium, in a vacuumchamber. To form the nitrides of the aluminum and/or zirconium, nitrogenis continuously supplied and removed in the appropriate fashion toadjust a reactive gas partial pressure as a controllable parameter forcontrolling the deposit procedure.

The system produced by that process has at least one layer whichcomprises covalent bonds of aluminum nitride or bonds of aluminumnitride and zirconium nitride.

It will be appreciated that the above-outlined composition of the systemaccording to the invention and the operating procedure for producingsame have been set forth solely by way of example and illustration ofthe invention and that various modifications and alterations may be madetherein without thereby departing from the spirit and scope of theinvention.

What is claimed is:
 1. A laminate system with a thickness of at least 50nm up to 6 μm and wherein at least one layer of the laminate systemconsists of covalently bonded Al—Zr—N with an atomic ratio of Al:Zr≦1.2. A laminate system of claim 1 wherein the atomic ratio of Al:Zr isbetween 0.5 and 0.7.
 3. A method of using a laminate system according toclaim 2 for at least a partial surface coating of a material.
 4. Alaminate system of claim 1 wherein the atomic ratio of Al:Zr.
 5. Amethod of using a laminate system according to claim 4 for at least apartial surface coating of a material.
 6. A laminate system of claim 1wherein the atomic ratio of Al:Zr is between 0.25 to 0.45.
 7. A methodof using a laminate system according to claim 6 for at least a partialsurface coating of a material.
 8. A method of using a laminate systemaccording to claim 1 for at least a partial surface coating of amaterial.